5 years leaching experiments to evaluate a modified bauxite residue. Part 2: Remediation of sulfidic mine tailings

Abstract ALTEO company produces approximately 300,000 tons per year of bauxite residue washed and dried in a press filter to give Bauxaline®, after extraction of the alumina. The study explored different ways of recovery and re-use for this residue, namely transformation into a vegetated soil, acid mine drainage depollution, and sulfide-mine tailings remediation. The Bauxaline® was so transformed into modified bauxite residue (MBR), with reduced alkalinity, salinity and sodicity, as described in part 1. The net acid generation potential of two mine tailings with 1 mole H+/kg (1.5% sulfide) and is 3.3 mole H+/kg (5.3% sulfide), respectively, were counterbalanced by the acid neutralising capacity of 10% MBR or 10% MBR plus limestone, or by limestone only, on the scale of 40 liters lysimeters. Six lysimeters were monitored for 5-years, to assess long-term emissions from treated materials. Vegetation was tested on various conditions and its impact on emission was evaluated. The emissions of sulfidic mine tailings treated with MBR and limestone were very low. The sulfidic mine tailings with limestone only showed some peaks of emission, probably due to coating of the calcite grain by ferric oxide, impeding contact of percolating water with the calcite. Vegetation grew in the treated tailings. This study demonstrated that elements of sulfidic mine tailings can be immobilised temporarily by the alkalinity of the limestone (reduction factor of the emissions of elements of 300 and 40 for the two mine tailings, respectively), but that alkalinity (of limestone and MBR), and the aluminium and ferric oxides (of MBR) are more effective and necessary for long-term immobilisation (reduction factor of 300 and 900, respectively).